(i) Field of the Invention
This invention relates to a hydraulic control system for vehicular automatic transmission, which is provided with an accumulator or accumulators.
(ii) Description of the Prior Art
Hydraulic control systems of vehicular automatic transmissions are usually provided with accumulators in oil conduits which supply operating oil to and from hydraulic servos of friction coupling elements of the transmission, thereby to adjust the varying characteristics of transmission torque capacity on engagement and release of the friction coupling elements for preventing shift shocks. The accumulator of this sort is usually constituted by a cylinder and a spring-loaded piston fitted in the cylinder and applied with a line pressure or a back pressure commensurate with the vehicle speed to produce a varying pressure with characteristics corresponding to the vehicle speed.
In this connection, the back pressure which is applied to the accumulator piston governs the characteristics of the transmission torque capacity of the friction coupling elements, so that it is desirable to vary the back pressure correspondingly to the torque of the engine output shaft.